This invention concerns a direct reading resistance measurement device and in particular an ohmmeter capable of measuring resistance values in circuits powered by unknown voltages.
Conventional direct reading ohmmeters furnish a low current through measuring probes which extend from the meters to touch the tested circuit. The resistance value of the tested circuit is determined as a function of that current and is usually indicated on a calibrated meter or digital display. While this ohmmeter performs satisfactorily in most instances, the presence of foreign voltages in the tested circuit will cause erroneous ohmmeter readings (false resistance values) and may even destroy the sensitive low current circuits and meter movements of conventional ohmmeters.
Accordingly, it is an object of my invention to provide an electrical measuring device which neutralizes the effect of a foreign voltage in a circuit whose resistance is being measured.
It is also an object of my invention to provide a direct reading ohmmeter which may be connected in conventional fashion via two probes across electrical devices in powered circuits for indicating the value of resistance between the probes and for nullifying the effects of foreign voltages.